In a magnetic data storage and retrieval system, a magnetic read/write head, or transducer, is used to read from or write to a data track on the disc. The magnetic read/write head is carried by a slider, which “flies” above the surface of the disc due to the air bearing force produced by the relative motion of the slider and the disc. The slider is formed with an air bearing surface to ensure that the slider flies at the desired fly height above the surface of the disc.
Sliders are typically manufactured in batch mode by forming an array of sliders on a common substrate, often called a wafer. The transducers are built on the substrate using a variety of thin film deposition techniques. The wafer is sliced to produce bars, with one row of sliders in a side-by-side pattern on each bar. The bars are then lapped to define a specified stripe height of the transducer, and to establish the air bearing surface (ABS). After the air bearing pattern is formed on the bars, they are sliced to produce individual heads or sliders. When a slider is finished, the volume of the transducer is typically much smaller than the volume of the substrate.
The portion of the transducer that is nearest the ABS is referred to as the pole tip region. The layers of the transducer, including those in the pole tip region, include both metallic and insulating layers. Thus, the pole tip region has different mechanical and chemical properties than the substrate which forms the slider. These differences in properties create several challenges that affect the manufacturing process. For instance, the layers of the transducing head are lapped at a different rate than the substrate. As a result, when an ABS of the slider is lapped or milled, differing amounts of the layers will be removed—resulting in an uneven ABS.
Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. This lapping process results in a Pole Tip Recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer. Positive PTR occurs when the distance between the ABS and the pole region is greater than the distance between the ABS and the substrate so that the pole region is recessed. Negative PTR may also occur when the distance between the ABS and the pole region is less than the distance between the ABS and the substrate, so that the pole region is protruding.
In order to establish adequate electrical performance for high areal density recording heads, it is desired to have a very low magnetic spacing between the head and the disc. PTR from machining (both lapping and ion mill etching) of the slider ABS is one of the key contributing factors in the spacing between the head and the disc. The PTR mean achieved during manufacturing directly adds to the head to disc spacing budget. Similarly, the standard deviation of PTR resulting from current manufacturing methods critically affects the head to disc clearance/contact margin. Specifically, negative PTR may result in contact between the transducer and the surface of the disc, which is highly undesirable.
There have been several efforts to control the manufacturing process to reduce the variation in PTR of sliders. One method of doing so involves measuring the PTR of each slider on a bar after the bar has been lapped. The average PTR of the bar is then calculated, and bars having similar average PTR are grouped together. Next, the bars with similar average PTR are ion milled together to obtain the desired stripe height. However, because these manufacturing methods are based on average PTR, the standard deviation in slider PTR has been unacceptably high.
As the data storage competition is continuous, particularly in light of the desire for high areal density, HMS is reaching 10 nanometers. In order to achieve HMS target and head mechanical reliability performance, a PTR distribution with a near zero mean and very tight standard deviation is required. Thus, there is a need in the art for an improved method of manufacturing sliders to achieve the desired PTR.